Mobile communication devices are in widespread use throughout the world, and in particular in the metropolitan regions of the world. The cost of these devices and communication service has decreased so much over recent years that they are nearly as common as landline telephone communications. To remain competitive manufacturers have added functionality to their mobile communication device product to distinguish their products over those of other manufacturers.
One feature that has proven popular is the so called push to talk or dispatch mode of communications. In addition to conventional mobile telephony service, referred to as interconnect calling, these devices and systems support dispatch calling. Dispatch calling is a half duplex mode of calling resembling two way radio or walkie talkie operation. Furthermore dispatch calling is controlled by a push to talk operation where, when the party, for example, presses a push to talk button and begins speaking. Therefore the dispatch mode requires a low call set up latency so as to be as near instantaneous as possible. At the receiving device, as soon as an incoming dispatch call is received, unlike an interconnect call, the receiving device, upon responding to the incoming call page from the communication system, quickly unmutes a loudspeaker and begins playing the received audio information without any action on the part of the user of the receiving device.
A variety of accessories are available for mobile communication devices, and one particular type that has proven popular recently is a wireless earpiece. A wireless earpiece is worn on a user's ear, and connects to the mobile communication device via local wireless link, such as that known by the name Bluetooth. Since these accessories operate wirelessly with the mobile communication device, they must have their own power source, but because they are worn on the user's ear, they must also be small, so a large battery cannot be used. Consequently it is desirable to operate the earpiece in low power mode as much as possible. One way to achieve power saving operation is to have the earpiece go into a “sleep” mode and check periodically to see if the mobile communication device is transmitting anything to it. Such operation works fine with interconnect calling because in interconnect calling, before any audio information is received, the user of the receiving device must first answer the call, which gives the mobile communication device time to wake up the earpiece to an active state. However, with dispatch calling, the latency in waking up the earpiece becomes critical. If the mobile communication device responds to the incoming dispatch call and the incoming dispatch call is set up before the earpiece is awake, a portion of the transmitted speech may be lost or not heard by the user. Therefore, there is a need to reduce the time it takes to wake up the earpiece from a low power state to an active state for handling dispatch calling.